ABSTRACT:
Immunohistochemistry is used to distinguish sarcomatoid malignant mesotheliomas (SMM) from spindle cell and pleomorphic carcinomas (SPC) but there are no guidelines on how to interpret cases that show overlapping or equivocal immunohistochemical findings. A systematic literature review of the immunophenotype of these lesions was performed and the experience with 587 SMM and 46 SPC at MESOPATH was collected. Data were analyzed with Comprehensive Meta-Analysis 2.0 software (Biostat, Englewood, NJ). There were insufficient data to evaluate the differential diagnosis between SPC and localized SMM or peritoneal SMM. Meta-analysis showed considerable overlap in the immunophenotype of these neoplasms and significant data heterogeneity amongst many of the results. Survival data from MESOPATH patients showed no significant differences in overall survival between SMM and SPC patients. Best available evidence was used to formulate several evidence-based guidelines for the differential diagnosis between pleural SMM and SPC. These guidelines emphasize the need to correlate the histopathological findings with clinical and imaging information. Diffuse SMM can be diagnosed with certainty in the presence of malignant spindle cell pleural lesions showing immunoreactivity for cytokeratin and mesothelial markers and negative staining for epithelial markers. Criteria for the interpretation of various other combinations of immunoreactivity for cytokeratin and mesothelial and/or epithelial markers are proposed. Localized sarcomatoid mesotheliomas can only be diagnosed in the presence of spindle cell malignancies that exhibit immunoreactivity for cytokeratin and mesothelial markers and negative immunoreactivity for epithelial lesions, in patients that show no multifocal or diffuse pleural spread and no evidence for extrapleural lesions.

ABSTRACT:
INTRODUCTION: Molecular and immunologic breakthroughs are transforming the management of thoracic cancer, although advances have not been as marked for malignant pleural mesothelioma where pathologic diagnosis has been essentially limited to three histologic subtypes. METHODS: A multidisciplinary group (pathologists, molecular biologists, surgeons, radiologists, and oncologists), sponsored by European Network for Rare Adult Solid Cancers/International Association for the Study of Lung Cancer, met in 2018 to critically review the current classification. RESULTS: Recommendations include: (1) classification should be updated to include architectural patterns and stromal and cytologic features that refine prognostication; (2) subject to data accrual, malignant mesothelioma in situ could be an additional category; (3) grading of epithelioid malignant pleural mesotheliomas should be routinely undertaken; (4) favorable/unfavorable histologic characteristics should be routinely reported; (5) clinically relevant molecular data (programmed death ligand 1, BRCA 1 associated protein 1 [BAP1], and cyclin dependent kinase inhibitor 2A) should be incorporated into reports, if undertaken; (6) other molecular data should be accrued as part of future trials; (7) resection specimens (i.e., extended pleurectomy/decortication and extrapleural pneumonectomy) should be pathologically staged with smaller specimens being clinically staged; (8) ideally, at least three separate areas should be sampled from the pleural cavity, including areas of interest identified on pre-surgical imaging; (9) image-acquisition protocols/imaging terminology should be standardized to aid research/refine clinical staging; (10) multidisciplinary tumor boards should include pathologists to ensure appropriate treatment options are considered; (11) all histologic subtypes should be considered potential candidates for chemotherapy; (12) patients with sarcomatoid or biphasic mesothelioma should not be excluded from first-line clinical trials unless there is a compelling reason; (13) tumor subtyping should be further assessed in relation to duration of response to immunotherapy; and (14) systematic screening of all patients for germline mutations is not recommended, in the absence of a family history suspicious for BAP1 syndrome. CONCLUSIONS: These multidisciplinary recommendations for pathology classification and application will allow more informative pathologic reporting and potential risk stratification, to support clinical practice, research investigation and clinical trials.

ABSTRACT:
Malignant mesothelioma (MM), is an intractable disease with limited therapeutic options and grim survival rates. Altered metabolic and mitochondrial functions are hallmarks of MM and most other cancers. Mitochondria exist as a dynamic network, playing a central role in cellular metabolism. MM cell lines display a spectrum of altered mitochondrial morphologies and function compared to control mesothelial cells. Fractal dimension and lacunarity measurements are a sensitive and objective method to quantify mitochondrial morphology and most importantly are a promising predictor of response to mitochondrial inhibition. Control cells have high fractal dimension and low lacunarity and are relatively insensitive to mitochondrial inhibition. MM cells exhibit a spectrum of sensitivities to mitochondrial inhibitors. Low mitochondrial fractal dimension and high lacunarity correlates with increased sensitivity to the mitochondrial inhibitor metformin. Lacunarity also correlates with sensitivity to Mdivi-1, a mitochondrial fission inhibitor. MM and control cells have similar sensitivities to cisplatin, a chemotherapeutic agent used in the treatment of MM. Neither oxidative phosphorylation nor glycolytic activity, correlated with sensitivity to either metformin or mdivi-1. Our results suggest that mitochondrial inhibition may be an effective and selective therapeutic strategy in mesothelioma, and identifies mitochondrial morphology as a possible predictor of response to targeted mitochondrial inhibition.